So, I have LONG been a fan of chiasmus structure ever since I bumped into it in studying anthropology.
I first learned of it a few decades back when I was getting my feet wet in ancient Levant region anthropology and learned that, for example, Hebrew scribes in the "golden era" of literature (~7th c BCE to 2nd c BCE) would write in a set of (commonly) 7 "acts" (or sections) and that 1 and 7 would be mirrors of each other, 2 and 6 would mirrors, 3 and 5 would be mirrors, and act 4 would mirror itself internally such that the second half would reverse the first half.

So whatever you did in a section that came first, you had to undo it in its related section that came later.
For example, in ye olde "good book" of Matthew (which is not, strictly speaking Hebraic scribal text, but someone within the region of Alexandria with an interest in new-wave Hebraic interpretations of an old 2nd c BCE fallout of the "rightful" Zadok priest line to the Hellenistic Hebrew priest line, which had subsequently migrated to Egypt and built an alternative "true" temple there) went quite a ways out of their way to borrow that format. And so you have, as I was highlighting this for, instances like the divine heir comes from the divine plane in the opening (descension) and then rises to the divine plane in the ending (ascension). Divine to Mortal <> Mortal to Divine.
That's a tiny, tiny, tiny example to clarify the meaning here (there's hundred more buried in that literature, Daniel is even quite a bit more filled, and likely was the blueprint Matthew was drawn up from - especially considering the favor of Daniel to the Zadok line propaganda).

One of my favorite things about Star Wars, in fact, is that it is also written as a chiasmus narrative.
(I've known this for quite some time, being a super dork on Star Wars, and also being someone who studies ancient literature, but this fellow does an AMAZING job of really examining it for folks who want to take a peek [Only registered and activated users can see links. Click here to register])

Anywho...on to music.
I've had it in my head for a long time to figure out a way to write a chiasmus structure into an album.
That is to say that if there were 7 songs on the album, 1 and 7 would be inversions of each other in scale and structure, and etc... down the line with 4 inverting on itself midway through.

This is incredibly challenging as to do something like this you have to hit every second mark exactly the same all the way through every song pair in reverse conceptual pattern, and in mirrored chordal progression.

While I'm not QUITE ready for that yet, working on this in my head over time caused a thought to accidentally collide into existence.
What if two songs were written to be one song, but neither song on its own?

Like Descartes Wax which he deduced was in summary none of its individual states, but an impossible collage of all states at once. In essence, the total description and nature of the wax was meta-ontological - or meta-physical.

So you would draft song 1 (PART A) and design it to run (for ease of reference) "left" to "right", intro-to-outro.
Then you would draft song 2 (PART B) and design it to run "right" to "left", intro-to-outro.

Then you would put them together to play simultaneously, but PART B would be playing in reverse, while PART A would be playing forward.
If you flipped it around, then PART B would be forward and PART A would be played in reverse.

HOWEVER, both PART A and PART B would be written intentionally to complete each other's chordal progressions and structures.
Either without the other would be technically incomplete, though functionally complete (like the wax candle of Descartes).

Here's some images to help wrap the head around this idea.
Now, these aren't final blueprints.
These are PURELY brainstorming sketches to understand the nature of my task.
From these, I'll work out more detail and specifics (for example, I probably won't be in C Major in reality, and I probably won't be using the chord progressions shown).

So let's look at the Chord Progression Mirroring firstly.
This diagram shows two sections.

The top section shows the concept of chordal position relationships, such that PART B is always starting its Chord on the third degree of PART A's Chord.

The bottom section shows the concept that I won't be making CHORDS in any one single instrument.
Instead, I'll be borrowing from early baroque method and MAKING the chords out of each instrument playing one note at a time.
So 6 instruments end up making 2 pairs of harmonized chords at any given moment (in concept).

Keep in mind that PART B is playing in REVERSE (backwards) while PART A is playing forwards, and that PART A is playing in REVERSE (backwards) while PART B is playing forwards.

What this image shows is that the structures are in reverse of each other as well.

Now that becomes REALLY challenging when you stop to realize that you have to have the CHORDAL concepts outlined above accomplished in REVERSE structural order of the whole song format, AND it can't sound like shit in either direction (playing PART A or PART B in the "forward" position).

The structure map, btw, is a basic styling here as a concept placeholder.
So you have an Intro, Section A, B, C, C.A (which is C with a reprise of A added to it).
The height of each block is the complexity or intensity of components involved (usually indicating more instruments involved, or that it's louder or more aggressive; while lower means fewer instruments or less loud/aggressive).
So C is the breakdown and C.A is the build back up, and the first time you hear B (in the forward position) you are hearing it "lighter" than you will again after C and C.A.

BUT, at the same time, you'll be hearing the OTHER song's B, for example, at its fullest at the same time that you'll be hearing the current "forward position" song's B at its softest.

You'll also note that this will require ensuring that B can cross into A compatibly chordally since A and B overlap at the beginning and end (think Canon in D as an example of how to go about overlaying reusable sections like that).

This would effectively create an entirely new genre in form, as it would be such that you have two songs in one in this form, and the specific point of it would be to create something which cannot be defined by any ONE state that you look at it. Indeed even the concept of "forward" becomes relative, and what the identity of the song is in that "forward" changes depending on which direction you choose to call "forward".

Just wanted to share this crack-head idea that I'll get to at some point (going to take a while to map out right).

Another challenge is that since one track is played in reverse while other is in forward, I'll have to make both in separate projects and then pull, say, PART B and A into a new project and then reverse PART B and align it exactly to PART A with both in wave file.
Meaning that I'll need to write B forward to end with the mind that I will be then reversing it when pulled in to combine with A.

Here's the result, which is the audio of that last image.
The mark in the middle is a chime that I added for the purpose of clarifying where we flip directions.
I slapped Part B in forward Part A in reverse right after Part A in forward Part B in reverse just so both directions could be heard.

The way it's set up isn't for a song at this point.
It's organized to show each part separately phonically, then combined just tonally, then in full with both sets of drums and tones.